A four-month tank experiment with Pacific oysters found that oyster presence stimulates phytoplankton, making photosynthesis the dominant process that removes carbon from the system. Although individual oysters respire and add some carbon, the community-level increase in photosynthesis can produce a net carbon drawdown. Moderate oyster densities delivered the best carbon-balance results, while very high densities reduced benefits. The research appears in the Proceedings of the National Academy of Sciences.
Study Finds Oysters Boost Photosynthesis and Can Net-Remove Carbon — Moderate Farming Best
A four-month tank experiment with Pacific oysters found that oyster presence stimulates phytoplankton, making photosynthesis the dominant process that removes carbon from the system. Although individual oysters respire and add some carbon, the community-level increase in photosynthesis can produce a net carbon drawdown. Moderate oyster densities delivered the best carbon-balance results, while very high densities reduced benefits. The research appears in the Proceedings of the National Academy of Sciences.
07:24 AM, 11/17/2025Environment
Oysters stimulate photosynthesis and can help draw down atmospheric carbon
A new four-month tank experiment with Pacific oysters (Crassostrea gigas) shows that oyster populations can stimulate phytoplankton growth, making photosynthesis the dominant process for carbon removal in the system. The China-based research team reported that, while individual oysters respire and produce some carbon when building shells, the broader ecosystem effect can lead to a net carbon drawdown.
How oysters influence carbon balance
Oysters provide several ecosystem services: they filter suspended particles and pollutants from water, sequester carbon in their calcium carbonate shells, and contribute organic-rich biodeposits that help form carbon-storing seafloor sediment. At the same time, oysters respire and release some carbon. To determine how these opposing processes balance out, researchers ran a controlled experiment using tanks with different oyster densities and monitored carbon levels and phytoplankton concentrations.
"At the ecosystem scale, photosynthesis is significantly enhanced and emerges as the dominant process," the researchers wrote in the study.
The experiment found that oyster presence at the community scale increased phytoplankton biomass across the water column. Because phytoplankton photosynthesize, they absorb dissolved CO2 and produce oxygen, and this enhanced photosynthetic activity was a major driver of net carbon removal in the tanks. The authors suggest that oyster filtration and nutrient recycling — for example, through biodeposits and excreted nutrients — likely help stimulate phytoplankton growth, though they call for more research to clarify the mechanisms.
Density matters
Importantly, the study found that very high oyster densities in confined areas reduced the net environmental benefit. Moderate stocking densities produced the most favorable carbon-balance outcomes, indicating that careful management is needed to maximize climate and ecological benefits from oyster farming.
Implications and next steps
The findings suggest that well-managed oyster cultivation could help coastal communities locally reduce atmospheric CO2 while providing food and habitat benefits. The authors emphasize the need for additional field studies and ecosystem-scale assessments to confirm whether these tank results hold in natural and commercial aquaculture settings. The full study is published in the Proceedings of the National Academy of Sciences (PNAS).